Automated plant control systems include a comprehensive set of algorithms, or software-definable process control routines, to control and monitor various processes within, for instance, a manufacturing facility. The control systems can be tailored to satisfy a wide range of process requirements globally or within specified portions of the facility. Conventionally, the control systems include a variety of modules, each having its own processor or firmware, linked together by communication buses to result in a distributed process control system. The distributed nature of the system affords high performance with the capability to expand the system incrementally to satisfy growth or modifications in the facility.
A first objective of automated plant management is to provide a process control scheme that synthesizes plant-wide control of all processes to thereby improve overall efficiency of the facility. Process control systems generally provide a means to create custom process control strategies, e.g., software-definable process control routines. In object-oriented programming environments, a complete control strategy may be built from smaller components called "blocks," "parameters," and "connections." A block is a software construct used to encapsulate the data and the algorithms of elemental control computations; parameters define the interface to individual pieces of data within the blocks; and connections allow data to flow between the parameters of blocks.
The basic function of a connection is to provide data flow between parameters of different blocks. Depending on design of a block algorithm, however, provision of simple continuity and data flow is not sufficient. Different block algorithms may require different elements of connection functionality. For example, although block algorithms generally have implicit knowledge about the type of passed data, some algorithms may require more than this implicit knowledge; some algorithms need explicit data type information to be provided by connection services.
In addition, some block algorithms may implement built in safety-handling, which requires knowledge of not only the value of passed data, but also status information that tells whether connection continuity has been maintained; in some cases, it is also necessary that status information distinguish different types of failures that can cause connectivity to be lost. Block algorithms which do not need explicit access to status or data type may still require predictable behavior of delivered data in the event that connection continuity is lost; such blocks need a useable "fail safe" value, which may be different for different data types, to be delivered.
Some block algorithms may require parameters that are connected in only a minority of process control strategies, or the blocks occasionally need connections, but they do not need explicit access to data type or status. In addition, some blocks may not be able allocate a dedicated resource for every parameter which may sometimes need a connection. The entire set of block algorithms must provide a user a configuration model in which parameters may be connected as needed by implementation-specific algorithms; a system for constructing process control schemes should allow the sharing of data between block algorithms in a manner which is convenient and which does not require the addition of blocks solely for the purpose of establishing a connection.
Therefore, what is needed in the art is a more powerful and flexible form of data access that achieves heterogeneous data flow connectivity between parameters of algorithm blocks in a distributed control system.